Ignition and combustion control



April 1, 1941. E. K. scoGGlN lE'rAl.

[G ITION AND COMBUSTION CONTROL Filed Feb. l0, 1939 Patented Apr. 1,

. iGNrr-ion AND coMBUsrIoNcoN'rnor.

sima x. swam' marnueses s. Denison, Min- -neapolia Minn.,

assigner: to kMirmeapolis- Honeywell Regulator Company, Minneapolis, lillnna corporation of Delaware Application reti-nary' 1o, 1939, serial No. 255,686,

(ci. 11o- 1) 4 Claims. Our invention relates to` a system for automatically igniting solid .fuel in combustion chambers,

wherein the igniting apparatus is controlled in response to a 'thermostat orequivalent instru ment.

Theprimary .object .of our) invention is to pro- .vide an `automatic system' for 'initiating combustion of solid fueland consequent heating in I [therein of a well known form familiar to those skilled in the art. The upper part of the side l walls of the retort Il has suitable openings I2 therein to-permit the-passage of air therethrough for purposes of combustion of the fuel I3. 'I'he furnace I may 'have a casing or jacket il enclosing it in a manner well known in the art.

` Numeral I5 designates an automatic stoker driven a combustion chamber whenever there'is a de" mand for combustion.

Another obiect is to provide an automatic 'system having means i'or automatically initiating ber inresponse to a demand for combustion, said means .remaining inactive if combustion is already present.'

Another object is `to provide an automatic fluid fuelred devicefor ignitin'g'solid fueLin stat -or the j Another object is to provide an automatically combustion of solid 'fuelin s. combustion'cha'mby an electric motor I6, the'stoker being of fa known type and having a hopper I1 into which the sol-id fuel is'loaded. The stoker I5 supplies solid fuel to theretort i-I through a passage or conduit Il within which may-be located a sere-.v conveyer or a conveyer `of -other suitable type. The motor .It driving the stoker also drives a blower for providingQforced draft for the furnace,

.a combustion chamber in respons'e to a thermocontrolled solid fuel igniting device controlled by heat of combustion so as to 'cause thel device to. remain inactivewhen combustionis present..

Another object is to provides.' gas' red solid fuel igniting devicek responsive-to a thermostat and a stack switch or-.the like for igniting solid fuel in' response to the, thermostat, the stack switch preventing operationpf the device if combustion already exists in the combustion chamber.

Another object is to provide a "solid fuel retort arranged in combination witlruid fuel ired means for igniting fuel in the'retort.

.Another object is to provide a solidfuel retort arranged in combination with 'fluid fuel-med means for igniting fuel in theretort, the ignitmg means being exterior of the combustion Space.

Another object is to provide a solid fuel reto'rt in combination with fluid :fuel ilred ignition trblled solid fuel supplying means for a :embustion'chamber in combination lv vith automatically controlled fuei'igniting means. The singleflgure of the drawing represents diagrammatically a stoker fired furnace systemem- Referring to the drawing,1we have represented vat il a portion of a stoker fired furnace which uiting-unit generally designated at 22 comprising the draft air being forced through a supply duct I l communicating with the space'around the retort il and underneath the grate I2.

Our invention I is primarily concerned with -means for automatically igniting the solid fuel in the -retort. For; this purpose we provide an iga gas `lzvurner'nozzleu'and an element-i125 projecting through a side wall of the retort, the arrangement of the burner Anozzle 24 and element in our particular invention may be called aj gas torch. The element 25 is so arranged that air forced into the space around the retort Il and the flame from the burner nozzle 24 are projected through the element 25 and directed'sov as to impinge directly on the solid fuel within theretort.v The burner nozzle-244 is supplied with gaseous fuelV through a conduitv 26 and in the conduit 26 is interposed a magnetic type gas control. valve 21. Adjacent. the extremity of' the burner nozzle 24 is a constantly burning pilot burner 28 which is continuously supplied with fuel through a tube 29 connected to the conduit 25 ahead of the control valve 2l. Adjacent the pilot burner 28 isa safety pilot generally designated atv 3l which takes the form of a. bimetal element 32 which is normally heated and exed into engagement'with a xed electrical contact 33. Whenever gas is admitted to the burner nozzle" 24 it is ignitedby the llame 'of the pilot burner28.

Our system is primarily controlled by a thermostat 35 responsive tothe temperature of air or other medium the temperature of which is affected by heat generated in the furnace I'. The thermostat 35 is of .a known type comprising abimetal element 36 arrangedzto actuate may be of'al conventional tylpe having a retort 55 two flexible switch blades 31 and 38:, the blade and the blade 38 cooperating with a fixed electrical .contact 40. The blades 31 and 38 engage their respective contacts sequentially, the blade 31 engaging contact 39 at a predetermined temperature which may be 70 for example, andthe blade 38 engaging contact 40 at a predetermined lower temperature which may :he 1 or 2 lower for example. Thermostat 35 controls a relay generally designated at 42 comprising the coil winding 43 which cooperates with an armature arranged to move switch blades 44 and 45 to the left into engagement with respective xed contacts 46 and 41 when the winding 43 is energized.

Numeral 50 designates generally a. control instrument which is of a known type comprising two mercury switches I and 52, both of which are actuable by a helical thermostatic element 53 responsive to the temperature within the combustion chamber as shown. Mercury switch 5I is normally closed and is only open when the temperature Within the combustion chamber reaches a relatively high value, this switch forming a high limit switch as presently will become apparent. Mercury switch 52 is only closed by element 53 when the temperature within the combustion chamber drops to a predetermined low value indicating that combustion has receded to such an extent that it would not recover upon the addition of fresh fuel to the retort. Instrument 50 might also be a stack switch rather than a switch directly responsive to the temperature within the combustion chamber.

Power is supplied to our system from line conductors 55 and 56 which may be connected to a suitable source of external power. Low voltage power for the various instruments and control devices is supplied by a step-down transformer 51 having a primary winding 58 and a secondary winding 59, the primary winding having a greater number of turns than the secondary winding. The primary winding 58 is connected to the line conductors 55 and 56 by wires 60 and '6I respectively.

In operation, the thermostat 35 automatically controls the heating apparatus so as to supply heat whenever there is a demand made by the thermostat. In other words, the supply of fuel to the combustion chamber is intermittent as determined by the thermostat vand these calls for heat may be of long duration and closely spaced or of short duration and more widely spaced depending upon the heating load imposed upon the equipment. When the load is relatively light and the periods during which the thermostat is not demanding heat are relatively long, the flre in the combustion chamber may go out entirely or may recede to such a low condition that it would not recover upon the addition of fresh fuel thereto. Assuming that the fire has gone out or has practically` gone out and the thermostat 35 indicates a demand for heat, upon this occurring .blades 31 and 38 will be in engagement with their respective fixed contacts and a circuit for relay 42 will lbe established as follows: from thermostat blade 31to contact 39, wire 62, mercury switch 5I, wire 63, safety pilot 3|, wire 64, secondary 59 of transformer 51, wire 65, relay co il 43, wire 66, fixed contact4ll, blade 38 back to blade 31. As soon as this circuit is established relay 42 is energized causing blades 44 and `45 to move to the left into engagement with fixed contacts 46 and 41. Engagement of 31 cooperating with xed electrical contact 39 blade 44 with contact 46 establishes a maintaining circuit for coil 43 as follows: from blade 31 to contact 39, wire 62, mercury switch 5I, Wire 63, safety pilot 3I, wire 64, secondary 59, wire 65, coil 43, wire 66, wire 61, fixed contact 46, blade 44 and wire 68 back to the thermostat 35. As Will be observed, this latter circuit is independent of blade 38 of the thermostat so that after having been energized relay 42 will not Ibe deenergized until the temperature rises to a value above at which blade 31 engaged contact 38. 'I'hus the thermostat 35 has a. fixed operating differential and operates in a manner whereby chattering of the relay due to insecurely made contacts is eliminated. As soon as blade 45 engages contact 41 a circuit for energizing the motor I6 and starting the stoker and blower into operation is completed as follows: from line conductor 55 to contact 41, blade 45, wire 69, motor I6, Wire 10, and wire 13 back to line conductor 56. As soon as motor I6 starts the supply of fuel to the retort and supply of draft air for combustion begins. At. the same time as motor I6 is energized a circuit is completed for energizing and opening valve 21--pro viding mercury switch 52 is closed, it being recalled that it was assumed that the fire was out or practically out when the thermostat indicated the demand for heating. The circuit for valve 21 is as follows: from line cpnductor 55 to fixed contact 41, blade 45, wire 69, wire 1I, valve 21, mercury switch 52, wire 12 an`d Wire 13 back to line conductor 56. 'Ihe opening of valve 21 admits fuel to the burner nozzle 24 where it is ignited by the pilot burner 28 and the ame from nozzle 24 and air forced into the space around the retort II are directed through the element 25 in the manner of a torch, the flame impinging directly upon the solid fuel inv the retort and serving to ignite it. As soon as l the temperature within the combustion chamber has risen to a predetermined value high enough to indicate assurance that combustion has properly been established, the element 53 will open the mercury switch 52 deenergizing the valve 21 and cutting off the supply of fuel to the burner 24. Operation of the stoker and the draft blower will of course continue as long as the relay 42 is energized. Whenever the thermostat 35 becomes satisfied blade 31 will separate from contact 39 deenergizing relay 42 and discontinuing operation of the motor I6. It will be observed that if the duration of time between thermostatic demands for furnace operation are relatively short the fire in all probability will not go out and under these conditions the mercury switch 52 will 'not be in closed position at the time the thermostat calls for heat. Thus if combustion already exists in the combustion cham'ber the igniting unit 23 will not be operated. Opening of the mercury switch 5I or of the safety pilot 3l will of course prevent energization of the relay 42 by thermostat 35.

From theforegoing it is' apparent that we have .provided a combustion control system for solid fuel having` means for igniting the fuel whereby personal attention to the apparatus is made entirely unnecessary. The need of building a fire in the furnace after it has gone out as done in the past iseliminated andthe necessity of opening fire doors and performing the various tasks incident to manually building a fire on the grate are avoided. It is a feature of our invention that the igniting means for the solid fuel are arranged c xterlorlyE of the combustion cham- Y prising a gas burner it is within the realm oi our invention to use other forms of fluid fuel burning igniting devices. The single embodiment of our invention disclosed is a preferred representative form but other forms, modifications and variations in the invention are within our con'- ltemplation Aand it is our intention that we be limited only in accordance with the scope of the appended claims rather than by our disclosure.

`We claim as our invention:

1. In apparatus of the character described, in combination', means forming a combustion chamber adapted' to contain a solidv fuel, means associated with said combustion chamber constructed and arranged for igniting solid fuel in said combustion chamber, control means comprising a condition responsive control instrument capable of indicating a need for combustion for controlling said second mentionedmeans whereby com'- bustion can be initiated in'response to said control means, and means indicative of the presence of combustion in said combustion chamber controlling said igniting means so arranged that said igniting means is inoperative in response to said control means if combustion already exists in said combustion chamber.

2. In apparatus ofthe character described. in combination, means forming a combustion chamber adapted to contain a solid fuel, means assotrol means, and means for terminating operation of said igniting means in response to a condition indicative of the presence of combustion, said last meansbeing so constructed and arranged thatl said igniting means is inoperative in response to said control means if combustion ailciated with said combustion chamber constructed y and arranged for igniting solid fuel in said combustion chamber, control means comprising a condition responsive controlinstrument capable of indicating a need for combustion for controlling said second mentioned means whereby combustion can vbe initiated in response to said conready exists'in said combustion chamber.

3. In apparatus of the character described, in

l combination, means forming a combustion chamber adapted to contain a solid fuel, means associatedwith said combustion chamber constructed and arranged for igniting solid fuel therein, means for feeding solid fuel to said combustion chamber, control means comprising a condition responsive control instrument controlling said fuel feeding means and igniting means whereby combustion can be initiated in said combustion chamber in response-to said control means, and means indicative of the presence of combustion in said combustion chamber so constructed and arranged that said igniting means is inoperative in response to said control means if combustion exists in said combustion chamber.

4. In apparatus of the character described, in combination, means forming a combustion chamber adapted to contain a solid fuel, means associated with said combustion chamber constructed and arranged for igniting solid fuel therein, means for feeding solidy fuel to said combustion chamber, control means comprising acondition responsive control instrumentv controlling said fuel feeding means and igniting means whereby combustion can be initiated in said combustion chamber in response to said control means, and

Ameans for terminating operation of said igniting means in response to a condition indicative of the presence of combustion, said last means being so constructed and arranged that said igniting means is inoperative in response to said control means if combustion already exists in said combustion chamber.

- ELMER. K. SCOGGIN.

FREDERICK S. DENISON. 

